Propylene/ethylene/1-hexene terpolymers are already known in the art for the production of pipes or films.
EP 483 523 relates to a compositions of crystalline polymers of propylene of this invention comprise (weight percentage):    A) 30-65%, preferably 35-65%, more preferably 45-65%, of a copolymer of propylene with a C4-C8 alpha olefin containing from 98 to 80%, preferably from 95 to 85%, of propylene;    B) 35-70%, preferably 35-65%, more preferably 35-55%, of a copolymer of propylene with ethylene, and optionally from 2 to 10%, preferably from 3 to 6%, of a C4-C8 alpha-olefin, said copolymer containing 2 to 10% ethylene, preferably from 7 to 9% when the C4-C8 alpha-olefin is not present, and 0.5 to 5%, preferably from 1 to 3% ethylene, when the C4-C8 alpha-olefin is present.
The C4-C8 alpha-olefin is preferably selected from 1-butene; 1-pentene; 1-hexene; 4-methyl-1-pentene; and 1-octene. Particularly preferred is 1-butene.
Better results in terms of seal initiation temperature can be obtained by using 1-hexene instead of the preferred monomer 1-butene in particular ranges.
WO2006/002778 relates to a pipe system comprising a terpolymer of propylene/ethylene and alpha olefin wherein the ethylene content is from 0 to 9% by mol, preferably from 1 to 7% by mol and the 1-hexene content ranges from 0.2 to 5% wt. The applicant found that it is possible to select from these ranges a composition having improved properties to be used for films.
U.S. Pat. No. 6,365,682 relates to propylene based terpolymers to be used for films. The ethylene content ranges generally from 1 to 10 wt % and the alpha olefin ranges from 5 to 25 wt %. for the preparation of films terpolymers having an ethylene content ranging from 0.9 to 3 wt % and an alpha olefin content ranging from 1 to 15 wt % is indicated. Only terpolymer of propylene/ethylene and 1-butene are exemplified. The applicant found that when 1-hexene is used in particular amount the characteristics of the films can be improved.
The applicant has now found that by using a particular polymerization process it is possible to obtain terpolymers having an high melting point, a vey low seal initiation temperature (SIT) at a relatively low content of comonomers. This allows obtaining films with improved features by using low amount of comonomers.